Over the course of its history, Israel has faced a series of attempts to uproot the Jewish people from its land, including terrorism and massive conventional armies. Today the main threat comes from thousands of rockets and missiles in the hands primarily of Hezbollah, Hamas and their patron Iran. Israel's development of missile defenses to counter this threat is a technological triumph, but also creates a set of strategic dilemmas. Because these defenses can reduce its own casualties almost to zero, how can Israel justify self-defense against rocket and missile attacks when its enemies launch these weapons behind human shields? This has real implications for Israel's deterrence against adversaries like Hezbollah and Hamas.

The first challenge, which began before the establishment of the state, was a civilian terror campaign. This campaign took various forms, but overall, consisted of a series of waves of terror that began with the arrival of the first Zionist immigrants at the end of the 19th century, continued through the attacks of 1921 and 1936, and the fierce battles held between the U.N. resolution on partition in November 1947 and the invasion of the Arab armies on May 15, 1948. After the establishment of the state, the terror campaign was less coordinated, lasting up until the first terror attack conducted by an organized movement, Fatah, in 1965. The waves of terror have continued with varying levels of intensity up to today, most recently in the form of "lone wolf attacks" with guns or knives.

The second challenge, interstate warfare, began with the end of the British Mandate, when the armies of seven Arab countries invaded the nascent Israel. These rounds of warfare continued over a 25-year period, with the last war against regular armies having taken place in 1973. Throughout the years since, up until the US invasion of Iraq and the Arab Spring, Israel was surrounded by millions of troops, tens of thousands of artillery pieces, thousands of tanks, and many hundreds of warplanes. Israel handed the Arab armies a series of resounding defeats on the battlefield, and thus wars of this kind became less attractive to Arab states.

The third, contemporary challenge is rooted in the failures of the civilian terror campaign and regular Arab armies against Israel. Now, Israel's opponents instead invested immense resources in large-scale firepower based on rockets and missiles. Following the Arab Spring, and the removal of the Syrian army as a threat to Israel, non-state combatant organizations-mainly Hezbollah, but also Hamas-have constructed most of their force around this type of firepower.

Today, Israel's civilian population is threatened by some 120,000 rockets and missiles. Most of them-over 100,000-are held by Hezbollah in Lebanon, while up to 5,000 rockets are deployed in Gaza by Hamas and Islamic Jihad. The remainder consist of several hundred ballistic missiles in Iran, and several hundred rockets held by Islamic State in Syria and the Sinai Peninsula.

Israel has invested significant efforts in shifting the balance of power against missiles and rockets. While all the rockets fired by Hezbollah in 2006 toward Israeli population centers found their targets; in 2014, 90 percent of the rockets fired by Hamas toward Israeli civilian targets, which Israel decided to defend, were intercepted by the Iron Dome active defense system.

This represents a revolution in Israel's ability to defend itself against the main threat to its armed forces and to its civilian and military home front. This is a first-rate technological achievement, which, together with the Arrow 2 system, provides Israel with a good level of defense. With the completion of the David's Sling system within the coming year, and of the Arrow 3 system within the next two years, Israel will be even better protected. We owe a great debt to American aid; but this success is founded on Israeli genius, originality, creativity, and of course a large-scale Israeli financial investment. This is an expensive project, at around $7-10 billion, in addition to the high-quality personnel required for the new defensive array.

Due to the drastic reduction in the number of casualties and the extent of destruction caused to Israel, active defense reduces the amount of pressure on Israeli leaders to wipe out enemy rocket and missile capabilities, and to do so as quickly as possible. Simply put, the success of Iron Dome has saved the lives of many of Israelis and much more of the Palestinians, because it has allowed the Israeli government and the IDF to be far more circumspect in the use of firepower. However, this success also brings with it some fundamental problems at the strategic policy level.

First, given that the number of interceptors is limited, where should the defense system be activated, and where should rockets "be allowed to fall" within Israel? This is a difficult question of priorities. Is it more important, in these kinds of operations, to protect the civilian population, or to protect the armed forces and military infrastructure so that the fight against the enemy can continue? It is clear that Hezbollah's main goal is to harm as many civilians as possible. It is necessary to take into account the pressure that can be expected from the civilian home front to defend them, but it is also clear that only the armed forces can shorten the war and strike at Hezbollah's launching capabilities. This creates very difficult trade-offs: where should the interceptors be allotted-to defend civilians, or to defend various elements of the military system? Should an attack on IDF headquarters in Tel Aviv be prevented, at the cost of a missile being allowed to hit the Bavli neighborhood a mile or two north of there?

Second, what are the implications of a reduced number of casualties on Israel's home front? This being the case, what would be the justification for Israel to inflict large losses on the other side? What are the international implications of such a situation, including legal considerations? I recently watched a public debate at Oxford, during which it was claimed that Israel is guilty of war crimes, with one of the most vocal arguments being the ratio between civilian casualties-according to the speaker, seven Israelis killed versus 1,500 Palestinians. The truth is that while Israel defends its citizens and invests boundless efforts toward this end, Hamas intentionally sacrifices its civilians, all of whom are "human shields" as far as it is concerned. Ironically, the world (or at least the gentleman from Oxford) would like to punish Israel for this. Both sides are successful in their efforts: Israel acts legally, and saves its civilians; Hamas acts illegally, yet the end result is that Israel's legitimacy is damaged. The irony would only be increased should a case be brought against Israel at the International Court of Justice, with any accusation of disproportionate use of force being essentially based on Israel's very success in defending its own citizens. This was not the intention of the authors of the relevant international conventions.

This problem will become even more evident if Israel goes on the offensive in order to strike at the other side's launch capabilities. If ground forces are deployed, there will be large numbers of casualties on the other side, many of them civilians, because these organizations operate from within civilian areas and among civilian populations. How can such a number of deaths be justified internationally while, due to active and passive defense systems, the number of Israeli civilian casualties will be very small? The terror organizations make cynical use of the naïve international audiences to fight Israel, with a great deal of success. This is particularly relevant concerning the next conflict with Hezbollah: ground forces will have to be used at some stage, given that the number of missiles they hold is too large to be dealt with solely by the interceptors Israel currently possesses.

There is a third dilemma. The Israeli government needs legitimacy from the populace for operations. If there are no civilian casualties or very few, will the government have the legitimacy to embark on military operations that may result in many soldiers being killed, in particular ground offensives?

These dilemmas give rise to some very important questions about Israel's ability to survive in this volatile region. There is a serious claim made that Israel's deterrent capabilities have reduced significantly because in this new situation, it is difficult for a government to take a decision that may endanger lives, especially with regards to deploying ground forces. Ironically, the success of the active defense systems provides a certain immunity for Israel's enemies, who know that embedding themselves sin civilian populations makes it harder to defeat their launch capabilities without the use of Israeli ground forces. It is the very success of Iron Dome, and of the other elements of the active and passive defense systems that ties Israel's hands from acting against its enemies, who feel less threatened and at greater liberty to use rockets and missiles.

Conclusions:

The success of Iron Dome has saved the lives of many of Israelis and much more of Palestinians, because it has allowed the Israeli government and the IDF to be far more circumspect in the use of firepower.

The more successful the active defense systems are, then ironically, the less legitimacy Israel has for acting to prevent the enemy firing on it. Enemy launchers are deployed within a civilian population, and any strike against them would result in a large number of civilian casualties, out of all proportion to the low number of Israeli casualties from enemy fire.

The question of legitimacy is even harder when it comes to the use of ground forces, when internal legitimacy also becomes a consideration for decision makers. Ground forces will have to be used at some stage against Hezbollah, given that the number of missiles they hold is too large to be dealt with by the interceptors Israel currently has, and these questions will be asked both domestically and internationally.

Israel must build four layers of defense against missiles, rockets and mortar fire (at all ranges), improve its ability to intercept increasingly accurate missiles, and be able to withstand lengthy rounds of warfare requiring very large numbers of interceptors.

Intelligent use of active defense and ground forces, and high readiness of the civilian home front - including advanced passive defenses like shelters and orderly evacuation of civilians from areas under attack - are necessary against the greatest conventional threat Israel will face in the next few years.

Maj. Gen. (ret.) Yaakov Amidror is a distinguished fellow at JINSA's Gemunder Center for Defense and Strategy. He is also the Greg and Anne Rosshandler Senior Fellow at the Begin-Sadat Center for Strategic Studies, and former national security advisor to the Prime Minister of Israel. He served 36 years in senior IDF posts, including commander of the Military Colleges, military secretary to the Minister of Defense, director of the Intelligence Analysis Division in Military Intelligence, and chief intelligence officer of the Northern Command.